1. Field of the Invention
The present invention relates generally to magnetic heads for hard disk drives, and more particularly to magnetoresistive read head elements of such magnetic heads.
2. Description of the Prior Art
A typical prior art read head portion of a magnetic head for a hard disk drive includes a plurality of thin film layers that are deposited and fabricated to produce a magnetoresistive read head sensor, as is known to those skilled in the art. In the typical fabrication process of this prior art read head, a plurality of sensor layers are first deposited across the surface of a wafer substrate. A photoresist mask is then applied to mask the read sensor layers in a central read head region for defining a read head sensor width. The unmasked sensor layers in side regions are then removed by ion milling. A magnetic bias layer stack, including electrical leads, is then deposited at the sensor edges in the unmasked side regions. The central photoresist mask is subsequently removed and an insulation layer, a magnetic shield layer and further layers and structures are then fabricated to complete the magnetic head. Due to shadowing effects of the mask and other problems in depositing the bias layers, it can be difficult to reliably achieve a designed read head sensor width, and inconsistent sensor quality can result.
Recently, a read head element has been developed where the masking and ion milling step is eliminated. In this read head design, the magnetic bias layers are deposited across the surface of the wafer on top of the read head sensor layers. A central portion of the bias layer is oxidized to remove its magnetic moment, where the outer portions of the bias layer are masked, and therefore are not oxidized. The outer, non-oxidized portions of the bias layer then provide a desired magnetic bias to the sensor layers, whereas the central, oxidized portion of the bias layer provides no biasing effect to the sensor layers disposed beneath it. As a result, the read head sensor layers in the central region remain sensitive to magnetic fields from data bits on a hard disk, whereas the outer portions of the sensor layers are desirably biased by the non-oxidized portions of the bias layers that are deposited upon them.
A problem that has developed with the recently developed read head element described above is that the oxygen within the oxidized central portion of the bias layer has been found to migrate or diffuse into adjacent layers, such as the insulation layer fabricated above it, when the magnetic head is subsequently heated for annealing purposes in subsequent magnetic head fabrication steps.